In institutional and industrial washing processes the wastewater of the washing process is usually cleaned and purified by using membrane filtration units. The obtained purified water can then be re-used in another washing cycle. The use of a membrane filtration process for the cleaning of wastewater results in a decrease of the amount of fresh water required to be added to the washing cycle and accordingly in a reduction of costs and saving resources. Also from an environmental standpoint the use of membrane filtration is meaningful.
However, the membrane cleaning processes can only be applied for wastewater which does not contain components blocking the membrane of the membrane filtration unit. Therefore it is necessary to use membrane-compatible detergents in these washing processes which do not contain any membrane-blocking or membrane-destroying components.
In the state of the art membrane-compatible detergent compositions are already known. However, most of these detergents are detergents in paste form having a high viscosity.
WO 2005/118760 A1 describes for example a membrane-compatible pasty soap composition which is used in a washing process in which the wastewater is purified by a membrane filtration unit and especially in a membrane filtration unit comprising one or more reverse osmosis steps. The detergent comprises anionic surfactants, non-ionic surfactants, an alkalinity source, and an organic and/or inorganic builder on a non-silicate basis. Furthermore the composition is free of greying inhibitors on a cellulose basis, silicates, and phosphates.
As non-ionic surfactants fatty alcohol alkoxylates are used which are ethoxylated and/or propoxylated. Furthermore the composition comprises alkyl polyglycoside having 8 to 14 carbon atoms.
The paste has a high viscosity which is preferably between 30,000 to 60,000 mPas at 50 revolutions per minute measured using a Brookfield rotational viscosimeter with spindle no. 7 at 25° C.
A further paste-like detergent is described in WO 02/46351 A1. This detergent is also used in a washing process in which the accumulated wastewater is cleaned by a filtration process using a membrane filtration unit.
The use of detergents in paste form in washing processes has the disadvantage that expensive dosing units are necessary to pump the high viscous paste into the institutional and industrial washing machines. Therefore there is a need for providing a liquid membrane-compatible detergent concentrate having low viscosity which can be pumped through the washing device by using standard pumping units which are less expensive.
In principle liquid detergents are known from the state of the art. Such detergents are for example described in U.S. Pat. No. 5,880,083, WO 2004/065535 A1, and WO 2004/041990 A1. However, the liquid detergents which are used in the state of the art often contain components which cause the blocking of the membrane filtration unit and hence cannot be used for washing processes in which membrane filtration units are used for the cleaning of the wastewater. Those components if used in high amounts are for instance cationic surfactants, certain emulgators, carboxymethylcellulose and silicates. These components immediately block the membrane and lead to an interruption of the whole washing process. By leaving such components out of the detergent composition the stability of the liquid detergent composition which is normally an emulsion or dispersion is decreased. This decreased stability results in a separation of the emulsion or the dispersion after storage or when used at extremely different temperatures. Separated emulsions or dispersions cannot be used in the washing process and cannot be dosed using the usual dosing units.
Therefore it is necessary to treat the separate phases in order to obtain the homogenous emulsion or the dispersion again. With some liquid detergents this is even not possible so that the separated emulsions or dispersions cannot be used any longer and have to be disposed.